Method for Zone Isolation in a Subterranean Well

ABSTRACT

A method is for zone isolation in a subterranean well. The well is provided with a pipe body at least in a portion. The method includes providing a plug over a longitudinal section of the well, the plug covering substantially the entire cross section of the well at least in a portion of the longitudinal section, so that the plug fills the inside, of a pipe body and an annulus between the outside of the pipe body and a surrounding well body.

The invention relates to a method for zone isolation in a subterranean well. More specifically, the invention relates to a method in which a balanced plug over a longitudinal section is established in the entire cross section of the well to prevent undesired production from a reservoir.

Isolation between zones in different production intervals is essential to be able to control and optimize the production from a subterranean well such as a petroleum well or a geothermal well. As a reservoir is being emptied and/or existing barriers for isolation between different zones are becoming weaker, the fluid flows within the reservoir may change so that the production decreases or, at worst, comes to a halt. For example, when a production interval is emptied of oil, the interface between water and oil may gradually be draw upwards and enter the producing zone, so-called coning, so that a flow of water completely or partially replaces the flow of hydrocarbons into the production string of the well. Gas coning may also occur. Barriers intended to prevent undesired fluid flows between different zones of a reservoir are subjected to great strains, in the form of powerful pressures and temperature differences among other things, hence intense tension and stress forces. It is known that this may result in damage to a cement barrier so that the integrity of the barrier is ruined. This may result in undesired fluid production behind casing and casing liners, among other things, and could further reduce or, at worst, make further production from the well impossible.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through features which are specified in the description below and in the claims that follow.

A method for zone isolation in a subterranean well, the well being provided with a pipe body, at least in a portion, characterized by the method including

(A) providing a plug over a longitudinal section in the well, the plug covering substantially the entire cross section of the well at least in a portion of the longitudinal section, so that the plug fills the inside of the pipe body and an annulus between the outside of the pipe body and a surrounding well body.

The pipe body may be, for example, a casing or a casing liner of types known per se and the pipe body may be part of a longer pipe string.

The surrounding well body may be another pipe body, or it may be the formation itself.

It is also known that a well plug may be established by means of a method and devices as proposed in the Norwegian patent application 20111641 entitled “Method for combined cleaning and plugging in a well, washing tool for directional washing in a well, and use of the washing tool” and by the Norwegian patent application 20120099 entitled “Apparatus and method for positioning of a fluidized plugging material in an oil well or gas well”, both filed in the name of the present applicant.

In a first embodiment, step (A) of the method may include the substeps of:

(A1) lowering a perforation tool into the pipe body to the longitudinal section where the plug is to be set; and

(A2) forming perforations in the pipe body along the longitudinal section by means of the perforation tool.

The perforation tool may be a perforation gun of a type known per se.

This may be appropriate in order to ensure good circulation of a plugging material from the inside of the pipe body out into the annulus on the outside of the pipe body. The perforation may be carried out in an undamaged/unperforated portion of the pipe body or in an already perforated portion of the pipe body if the number, distribution and design of the perforations are not sufficient to ensure god circulation for subsequent washing and plugging. A preferred distribution of the perforations in the pipe body may be in the order of 12 per foot in a 135/45 degrees' phase within said longitudinal section.

In a first embodiment of the method, the plug may remain set in the entire cross section of the well. This may be advantageous in, for example, a case in which a barrier element set earlier has lost its integrity and there is undesired fluid production behind a casing or a casing liner from a part of the formation below. Thus, a plug covering the entire cross section could isolate the formation, from which the undesired fluid production is coming, from the rest of the well.

In addition, or as an alternative, step (A) of the method may include the following substeps:

(A3) by means of a washing tool which is attached to a string allowing through-flow and which is lowered to the longitudinal section, pumping a washing fluid down the string and out into the pipe body via the washing tool;

(A4) by means of a directional-control means connected to the washing tool, directing the washing fluid into the annulus between the outside of the pipe body and the surrounding formation; and

(A5) pumping a fluidized plugging material down the string and out into the pipe body, and thereby also into the annulus via the perforations in the pipe body.

Further details about the substeps A1-A5 and also about said washing tool can be found in the above-mentioned Norwegian patent application 20111641.

It may be an advantage if a displacement member in the form of a pressure apparatus as described in the Norwegian patent application 20120099 mentioned is used to further displace and distribute the fluidized plugging material in the casing and further out into the annulus.

In one embodiment of the method, the steps of perforation (A2) and washing (A3, A4) may be carried out in separate trips down the well.

In another embodiment of the method, the steps of perforation (A2) and washing (A3, A4) may be carried out in one and the same trip into the well. A combined perforation and washing apparatus is described in the Norwegian patent application 20111641 mentioned. The perforation tool and the washing tool may be releasable in combination or individually from the string.

In one embodiment, the method may further include leaving the perforation tool in the well. This may be practical to save operation time if the perforation tool can be “hidden” in the well and/or if the perforation tool is a drillable one.

As an alternative, or in addition, the method may further include leaving the washing tool in the well. This may be advantageous in order to save operation time and/or to use the washing tool as a base for the plug that is to be established. It may be advantageous if the washing tool is a drillable one.

In a second embodiment, after step (A), the method may include the step of: (B) drilling out a centrally through-going portion of the plug, so that at least a cross-sectional portion of the plug on the outside of the pipe body remains. This may be desirable in a case in which there is to be production from a part of the well lying below the plug and the well path therefore has to be opened up again.

As an addition to said first or second embodiment, the method may include providing one or more perforations in a portion of the pipe body outside the longitudinal section in which the plug has been set. This may be necessary if existing production perforations have been blocked or closed off from the rest of the well in connection with the isolating.

The fluidized plugging material may be, for example, cement slurry, unconsolidated mass or a combination thereof.

In what follows, examples of preferred embodiments are described, which are visualized in the accompanying drawings, in which:

FIGS. 1-8 show, in side views, simplified schematic sections of a well in different stages in accordance with a first embodiment of the method of the present invention; and

FIGS. 9-10 show, in side views, simplified schematic sections of a well in different stages in accordance with a second embodiment of the method of the present invention.

In what follows, the reference numeral 1 indicates a subterranean well as used in the method of the present invention. The well 1 has been drawn in a schematic and greatly simplified manner, and well elements which are not central to the invention may have been left out of the drawings. Well fluids and cement barriers already established, which will be known to a person skilled in the art, are not shown in the figures. A casing 21 extends down the well 1, forming a radial boundary between a well path 2 and a surrounding formation 7. A pipe body 211 in the form of a casing liner is hung from the lower portion of the casing 21, extending down into a producing part of the well 1. The casing liner 211 is formed with perforations 212, through which fluids may flow from the formation 7 into the well 1. A connection pipe 210 and the casing liner 211 together form a pipe string which extends throughout the length of the well 1. In the exemplary embodiment shown, the pipe string is formed with one and the same inner diameter. The purpose of the method of the present invention is to isolate formation zones, from which undesired fluids are entering the well 1, from the rest of the well 1, whether it be undesired fluid flow through producing perforations 212 as shown in the FIGS. 1-8, or undesired fluid flow behind casing 21 or casing liners 211 as shown in the FIGS. 9-10.

In FIG. 1, a producing well 1 is shown. An interface between water and oil has been drawn upwards and into the producing zone of the formation 7, so that an undesired flow of water, indicated by arrows in towards the perforations 212, has completely or partially replaced the flow of hydrocarbons into the well 1. To remove or at least reduce the undesired water flow into the well 1, there is a wish to isolate the zone, from which the undesired production is coming, from the rest of the well 1. The reference numeral 221 indicates a safety/production valve of a type known per se.

FIG. 2 shows the well 1 after a perforation tool 33 has been lowered into the casing liner 211 and placed along a longitudinal section L1 opposite the perforations 212. The perforation tool 33 may be a perforation gun of a type known per se. The perforation tool 33 is used to form new perforations 213 in the casing liner 211 which is to be used in subsequent washing and plugging as shown in FIG. 3. In a case in which the existing perforations 212 satisfy the requirements for design, position and density as required in the subsequent washing and plugging operations as described above, it will not be necessary to form new perforations 213. FIG. 3 shows the well 1 after the string 3 with the perforation tool 33 has been pulled out and new perforations 213 have been formed in the casing liner 211.

A combined washing and plugging tool 35 is then lowered into the well 1 within the casing liner 211 as shown in FIG. 4. Perforation and cleaning and plugging may be carried out in the same trip or in separate trips down the well 1. A washing fluid not shown is carried through the string 3, into the casing liner 211 and further out into an annulus 5 via the perforations 213. It may be an advantage if the washing fluid is directed substantially radially into the annulus 5 by means of a directional-control means 351, as described in the Norwegian patent application 20111641. A washing fluid at great velocity may remove various particles, deposits and remains from earlier downhole operations, so that a fluidized plugging material which is subsequently to be carried into the annulus 5 may flow freely and be adhered in a better way. Then the fluidized plugging material is pumped through the string 3 and out into the casing liner 211 and thereby also into the annulus 5 via the perforations 213 in the casing liner 211, so that a plug 25 is formed over the longitudinal section L1, as shown in FIG. 5. At least in a portion within the longitudinal section L1, the plug 25 of cured plugging material extends over the entire cross section T1 of the well 1. It may be an advantage if an apparatus as described in the Norwegian patent application 20120099 is used in order to further displace and distribute the fluidized plugging material in the casing liner 211 and out into the annulus 5. The latter apparatus is not shown in the figures connected to the present document.

In FIG. 6, the well 1 is shown after a central through-going portion of the plug 25 has been drilled away by means of a drilling tool 31. A cross-sectional section T3 of the plug 25 outside the casing liner 211 is left inside the longitudinal section L1. The remaining cross-sectional section T3 of the plug 25 outside the casing liner 211 forms a barrier 51 in the annulus 5 between the casing liner 211 and the formation 7, thereto by isolating the well 1 from the reservoir zone from which the undesired water production was coming.

FIG. 7 shows the well 1 after it has been fully isolated for the above-mentioned purposes, whereas FIG. 8 shows the well 1 after new perforations 214 have been formed in the casing liner 211 at a distance from the longitudinal section L1 so that there may be production from another zone without undesired water drive. The distance between the longitudinal section L1 and the new perforations 214 may be very large, maybe in the order of kilometres.

FIG. 9 shows a well 1 in which an undesired water flow, indicated by arrows, is coming from a formation zone below the production zone and is flowing in behind the casing liner 211. This may quite possibly be a result of an earlier poor and/or difficult cementation job. There is therefore a need for new zone isolation. A plug is set in the entire cross section of the well, as shown in FIG. 10, in a portion below perforations 212 already producing, by means of steps indicated in the FIGS. 2-5. The plug 25 isolates the well 1 from the zone from which the undesired water production was coming and the production may be resumed via the perforations 212 existing already. 

1. A method for zone isolation in a subterranean well, the well being provided with a pipe body, at least in a portion, the method comprising: (A) providing a plug over a longitudinal section of the well, the plug covering substantially the entire cross section of the well at least in a portion of the longitudinal section, so that the plug fills the inside of the pipe body and an annulus between the outside of the pipe body and a surrounding well body, wherein (A) comprises: (A1) lowering a perforation tool into the pipe body to the longitudinal section where the plug is to be set: (A2) forming perforations the pipe body along the longitudinal section the perforation tool; (A3) with a washing tool which is attached to a string allowing through-flow and which is lowered to the longitudinal section L1, pumping a washing fluid down the string and out into the pipe body via the washing tool; (A4) with a directional-control means connected to the washing tool, directing the washing fluid into the annulus between the outside of the pipe body and the surrounding well body; and (A5) pumping a fluidized plugging material down the string and out into the pipe body, and thereby also into the annulus the perforations in the pipe body.
 2. The method in accordance with claim 1, wherein a displacement member is used to further displace and distribute the fluidized plugging material in the pipe body and further into the annulus.
 3. The method in accordance with claim 1, wherein perforation (A2) and washing (A3, A4) are performed m separate trips down the well.
 4. The method in accordance with claim 1, wherein perforation (A2 ) and washing (A3, A4) are performed in one and the same trip down the well.
 5. The method in accordance with claim 1, wherein the method further includes leaving the perforation tool in the well.
 6. The method in accordance with claim 1, wherein the method further includes leaving the washing tool in the well.
 7. The method in accordance with claim 1, wherein, after (A), the method comprises: (B) drilling out a central, through-going portion of the plug, so that there is at least a cross-sectional section of the plug left on the outside of the pipe body.
 8. The method in accordance with claim 1, wherein the method includes providing one or more perforations in a portion of the pipe body in a portion outside the longitudinal section in which the plug has been set.
 9. The method in accordance with claim 1, wherein the fluidized plugging material includes cement slurry for the formation of a cement plug.
 10. The method in accordance with claim 1, wherein the fluidized plugging material includes unconsolidated mass for the formation of an unconsolidated-mass plug. 